Catalysts for the addition polymerization of unsaturated organic compounds



Patented Nov. 6, 1945" CATALYSTS FOR THE ADDITION POLYMER- IZATION COMPOUNDS OF UNSATURATED ORGANIC William D. Stewart, Akron, Ohio, asslgnor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application April 15, 1942,

Serial No. 439,102 a 11 Claims.

This invention relates to the polymerization of unsaturated organic compounds which are capable of undergoing an addition polymerization to form high molecular weight linear polymers and particularly to the polymerization in aque ous emulsion of a butadiene-l,3 either alone or in admixture with a monomer copolymerizable therewith. The principal object of the invention is to provide a new class of catalysts or accelerators-i'or such 'polymerizations by. the use of which improved polymers are obtained in increased yield and in a much shorter interval of time.

I have discovered that the time required to effect addition polymerization reactions can be greatly reduced by the use of heavy metal catalysts and that the polymers produced when employing such catalysts exhibit excellent properties despite the short periods oi time required for the completion oi the polymerization. Certain oi these heavy metal catalysts, called redox systems because of their property oi catalyzing biological oxidation-reduction reactions, 'are disclosed in my copending applications Serial Nos. 379,712 to 379,717 inclusive, filed February 19, 1941 This application is a continuation-impart of my copending application Serial No. 379,714 and relates to the class of heavy metal catalysts derived from a heavy metal compound and an allphatic polycarboxylic acid containin at least two carboxyl groups and no additional types oi substituent groups other than hydroxy and primary amino groups. Typical acids included in this class are oxalic acid,

and other polycarboxylic acids containing two carboxyl groups connected together by an alkylene, alkenylene alkynylene or a hydroxyaminoor carboxy-substituted alkylene, alkenylene or alkynylene group such as malonic, succlnic, glutaric, sebacic and adipic acids, all of which conkylene radicals and citric acid which contains two carboxy groups connected by an alkylene radical having a hydroxy and a carboxy substituent.

The term heavy metal" is used herein tosigniiy metals which have a density greater than four, anatomic weight greater than forty and a low atomic volume (ratio of atomic weight to density) and consequently. appear substantially at or near the minimum points above an atomic weight of forty on Lothar Meyer's atomic volume curve; (See any standard textbook of Inorganic Chemistry such as Ephraim's Textbook of Inorganic Chemistry" page 30 or Caven and Lander's Systematic Inorganic Chemistry" facing page 30). The term heavy metal" includes therefore the metallic elements appearing in the center positions of the long periods of a periodic table arranged in long and short periods, and especially those occurring in the 6th to 12th positions of the long periods (considering the alkali metals to occupy the first position and all the rare earth metals to occupy a single position), that is, the elements occurring in group VIII of the Mendelyeevs Periodic Table such as groups I and II of the Mendelyeevs Periodic Table such as copper, zinc and mercury and those in subgroup A of groups VI and VII of the Mendelyeev's Periodic Table such as chromium, manganese and molybdenum.

The heavy metal catalysts of this invention are derived from a heavy metal compound and a polycarboxylic acid of the type described, and may consist oi complex compounds containing a heavy metal atom united to one or more polycaras in the complex compounds sodium ierri oxsimple heavy metal salts of polycarboxylic acids tain two carboxy groups connected by an alkylene radical; maleic and iumaric acids which contain two carboxy groups connected by an alkenylene radical; acetylene di-carboxylic acid which contains two carboxy groups connected by an alkynylene radical; malic, tartaric, hydroxy-fumaric and dihydroxy-maleic acids all or which contain two carboxy groups connected by hydroxy-substituted alkylene or alkenylene radi-, cais; tricarballylic and aconitic' acids which contain two carboxy groups connected by carboxysubstituted alkylene or alkenylene radicals; glutamic and aspartic acids which contain two carboxy groups connected by amino-substituted alor oi mixtures of heavy metal salts and polycarboxylic acids or polycarboxylic acid salts. In the latter event, the heavy metal salts may combine chemically with the polycarboxylic acids as theii salts to form complex compounds of the type described above, but it is to be understood that all catalysts obtained by the combination of heavy metal compounds and polycarboxylic acids of tions (i. e., in group VIII, I-B, II-B, VI-A and VII-A) of the firstlong period of the periodic table, and from polycarboxylic acids containing less than six carbon atoms, examples of such preferred catalysts being formed from mixtures of simple salts of iron, cobalt, nickel, zinc and copper with succinic acid, furnaric acid, tartaric acid and di-hydroxy-maieic acid. Since the polymerization reactions catalyzed by the method of this invention are preferably carried out in aqueous emulsion it is also highly desirable that the catalysts be water soluble, by which is meant that the whole catalytic system will dissolve in the amount of water Dresentin the emulsion.

The preferred catalytic combinations mentioned above are readily soluble in water when the heavy metal .salt employed is a nitrate, chloride, sulfate or other water soluble salt and when the polycarboxylic acid is employed as such or as an alkali metal salt.

In the practice of this invention addition polymerizations of unsaturated organic compounds to form high molecular weight linear polymers are preferably carried out in aqueous emulsion in the presence of the above-described heavy metal catalysts although other method of polymerization such as polymerization in homogenous systems may also be employed. In the emulsion polymerization process. the unsaturated compounds, or monomers, to be polymerized are emulsifled in water with the aid oian emulsifying agent and polymerization is then eflected by adding a heavy metal catalyst described above, together, if desired with various other substances, the nature of which will be described hereinafter, and then agitating the emulsion until polymer is formed. The resulting polymerized emulsion containing polymer particles dispersed in water greatly resembles natural rubber latex and may be coagulated in the usual manner to yield the solid polymer.

The amount of the catalyst to be used in the polymerization may be varied somewhat depending upon the particular catalyst used and the particular compounds polymerized but, in general, only very small-orcatalytic amounts are employed and it is preferable that no more than about 2% by weight, based on the weight of the monomers, of the whole catalytic system, including both the heavy metal compound and the polycarboxylic acid, if a mixture oi these is employed as the catalyst, be used. When the catalyst consists of a complex compound, containing a heavy metal atom united tonne or more polycarboxylic acid molecules, added as such, or of a heavy metal salt of a polycarboiwlic acid added as such, amounts of 0.1 to 1% of the catalyst are preferred. When,

however, the catalyst is added as a mixture of a heavy metal salt and a polycarboxylic acid or one of its alkali metal salts amounts of 0.01 to 0.1% of the heavy metal salt and 0.2 to 1.5% of the polycarboxylic acid or polycarboxylic acid salt give best results. Although ionizable heavy metal salts,' particularly those of copper and manganese. when present in polymerization batches not containing a compound which forms a complex therewith, often inhibit polymerizations unless their concentration is less than 0.1%, the catalysts oi thisinvention do not possess this disadvantage since the presence of the dicarboxylic acid converts the heavy metal ions into complexes in which the heavy metal atoms are present in a substantially un-ionized form.

As has been mentioned hereinabove the heavy metal catalysts of this invention may be used generally in the polymerization of those unsaturated organic compounds which undergo addition polymerizations to form high molecular weight linear polymers by which is meant that a large number of monomer molecules add onto one another to form a large molecule having a predominantly linear structure. Unsaturated organic compounds which undergo such polymer-- izations generally contain the characteristic structure and, in most cases, have at least one of the disconnected valencies attached to an electronegative group, that is, a group which increases the polar character of the molecule such as a chicrine group or an organic group containing a double or triple bond such as vinyl, phenyl, nitrile, carboxy or the like. Included in this class of monomers are the conjugated butadlenes or butadienes-l,3 such as butadiene (butadiene-1,3 2,3-dimethyl butadiene-1,3, isoprene, chloroprene, piperylene, 8-iuryi butadiene-1,3, B-methoxy butadiene-1,3 and the like; aryl oleflns such as styrene, p-chloro styrene, p-methoxy styrene, alpha-methyl styrene. vinyl naphthalene and the like; acrylic and substituted acrylic acids and their esters, nitriles and amides such as acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl alpha-chloro-acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl ethacrylate, acrylonitrile, methacrylonitrile, methacrylamide and the like, methyl isopropenyl ketone, methyl vimrl ketone, methyl vinyl ether, vinylethinyl alkyl' carbinols, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl iurane, vinyl carbazole, isobutylene, vinyl acetylene and other unsaturated hydrocarbons, esters, alcohols, acids, ethers, etc., of the type described. Such unsaturated compounds may be polymerized alone, in which case simple linear polymers are formed, or mixtures of two or more of such compounds which are copolymerizable with each other may be polymerized to form linear copolymers.

The catalysts of this invention are particularly efiective when the monomeric material polymerized is a conjugated butadiene or a mixture of a conjugated butadiene with lesser amounts of one or more other compounds containing a group which are copolymerizable therewith such as aryl oleiimi, acrylic and substituted acrylic acids, esters, nitriles and amides, methyl isopropenyl ketone, vinylidene chloride and similar compounds mentioned hereinabove. In this case the products of the polymerization are high molecular weight linear polymers and copolymers which are rubbery in character and may be called synthetic rubber. The polymerization of other monomers and monomer mixtures of the type described to form linear polymers of a resinous character is also improved, however, by the catalysts of this invention.

As emulsifying agents which may be employed in emulsion polymerizations may be mentioned soaps such as sodium oleate, potassium paimitate and sodium myristate, synthetic saponaoeous I materials including hymoial sulfates and alkaryl complete after 23 hours.

conditions, the salts of organic bases under acid conditions and the synthetic saponaceous materials under acid, alkaline or neutral conditions.

Polymerization initiators which are preferably,

although not necessarily. employed in the poly merization batch together with the heavy metal catalysts of thi invention include per-compounds such as hydrogen peroxide, benzoyl peroxide, potassium persulfate, sodium perborate, potassium percarbonate and the like as well as other types of initiators such as diazoaminobenzene, sulfurdi-.

oxide, dipotassium diazomethane disulfonate and triphenylmethylazobenzine. The per-compounds, particularly hydrogen peroxide when used with a fatty acid soap as the emulsifying agent, give especially good results in the emulsion polymerization of conjugated butadienes in the presence of combinations of heavy metal salts and amino acids as catalysts.

It is also desirable in the emulsion polymerizaand 0.35 part of glutamic acid. The polymerization requires only 14 hours to produce a 91% yield of a synthetic rubber similar to that ob tained in Example I.

Example IV v A mixture of 55 parts by weight of butadiene and 45 parts by weight of acrylonitrile is agitated at 30 C. in an aqueous emulsion containing 250 parts of a 3% aqueous fatty acid soap solution and a heavy metal catalyst comprising 0.05 part .of cobalt chloride and 1 part of the sodium salt of fumaric acid. After 71 hours there is obtained a 91% yield of a rubbery butadiene acrylonitrile copolymer which when compounded and ,vulcanized in a standard test recipe produces a vulcanizate having a tensile strength of over 5000 lbs/sq. in. and a 640% ultimate elongation. It is tion of conjugated butadienes to form synthetic 1 Example I A mixture of 55 parts of butadiene and 45 parts of acrylonitrile is emulsified in 250 parts of a 2% aqueous solution of myristic acid which is 85% converted into soap by neutralization with sodium hydroxide. 10 parts of a 3 solution of hydrogen peroxide, 0.3 part of a polymerization modifier, di-isopropyl dixanthogen and a heavy metal catalyst consisting of a mixture of 0.05 part of ferrous ammonium sulfate and 0.50 part of succinic acid are added to the emulsion and the emulsion is agitated at C. After 23 hours'a latex is obtained which, upon coagulation, yields 94 parts of a rubbery copolymer of butadiene and acrylonitrile. A similar polymerization in which no heavy metal catalyst is employed requires hours to produce a 94% yield and is only 45% The solubility and plasticity of the rubbery copolymer prepared in the presence of the heavy metal catalyst is equal to that of the polymer prepared in the absence of the catalyst and the vulcanizates obtained from the polymer prepared in the presence of the catalyst possess higher tensile strengths and ultimate elongations than similar vulcanizates from the polymer prepared in. the absence. of the catalyst.

Example II An emulsion of a mixture of butadiene and acrylonitrile is prepared as in Example I, except The procedure of Example I is again repeated using as the heavy metal catalyst a mixture 0.03

part of iron sulfate, 0.01 part of cobalt chloride to be noted in this example that no polymerization initiator such as hydrogen peroxide, potassium persulfate or the like is employed in the emulsion yet a good yield of a valuable polymer is obtained after only 71 hours. When the cobalt chloride-fumaric acid catalyst is not present in the polymerization recipe it is impossible to obtain a satisfactory yield of polymer unless at least a.week is allowed for the polymerization. Moreover, when using cobalt chloride alone as the cat- 'alyst only an 81% yield is obtained in 101 hours.

Example V A monomer mixture containing 2.5 grams of styrene and 7.5 grams of butadiene is emulsified with 25 c. c. of a 2% aqueous sodium lauryl sulfate solution in the presence of 0.035 gram of hydrogen peroxide, 0.03 gram of a polymerization modifier, 0.20 gram of sodium pyrophosphate and 0.1 gram of iron succinate. The polymerization of this emulsion requires 63 hours at 30 C. to yield 99% of a rubbery copolymer of butadiene and styrene. A similar emulsion not containing iron succinate requires 110 hours at 30 C. to produce-an 82% yield.

Example VI An emulsion containing the following ingredients is prepared:

Parts Butadiene 70 Styrene 30 Sodium myristate (2% aqueous solution) 250 The emulsion is then agitated at 30 C. for 87 hours whereupon a synthetic latex is obtained which, when coagulated,'produces an 89% yield of a rubbery copolymer. The copolymer is plastic and easily milled and may be compounded and vulcanized to form strong elastic vulcanizates. When a similar emulsion is polymerized without the addition of ferrous ammonium sulfate and succinic acid over 150 hours is required to complete the polymerization and when ferrous ammonium sulfate alone is used the polymerization is only 50% complete in 87 hours.

When this example is repeated using methyl acrylate, methyl methacrylate, methyl isopropenyl ketone, vinylidene chloride and other monomers in place of styrene similar synthetic rubbers are obtained in good yields in about the same length of time. The proportions of the monomers polymerized may also be varied without appreciably affecting the length of time re quired for the polymerization." For example a monomer mixture consisting of 90 parts oi styrene and parts of butadiene may be polymerized in this same manner in about the same timeto produce a strong. flexible. thermoplastic synthetic resin; Other thermoplastic resins may be obtained by using styrene, methyl methacrylate, vinyl chloride or the like alone or in admixture with each other as the polymerizabie material.

Other embodiments of theinvention in which various other heavy metal catalysts are used with various monomermixtures, initiators and emulslrying agents also demonstrate that the polymerization velocity is remarkably increased by the practice oi. this invention.

The use of the heavy metal catalysts of this invention is particularly important in the commercial manufacture of polymers since the great accelerating effect of these catalysts more than counteracts the inhibiting efiect of other substances which may be present during the polymerization. Many such inhibiting substances are quite difiicult to exclude from the polymerization batch because they may be present as impurities in the monomers or in other essential materials. Moreover other substances which it is highly desirable to include in the polymerization recipe, such as certain polymerization modifiers, also often retard the speed of the polymerization but when used with heavy metal catalysts the polymerization takes place in a convenient interval of time.

Other methods and procedure known to be useml in connection with the polymerization of unsaturated organic compounds are within the spirit and scope of the invention as defined in the appended claims.

I claim:

1'. The method which comprises subjecting a monomeric material comprising a conjugated butadiene, to polymerization in aqueous emulsion in the presence of a heavy metal catalyst obtained by the combination of a water soluble heavy metal salt and an aliphatic polycarboxyiic acid containing from two to three carboxyl groups and no additional structure other than aliphatic structure in which there is present, in addition to hydrocarbon structure, no structure other than hydroxy.

2. The method which comprises subjecting a monomeric mixture of a conjugated butadiene and another compound which contains a group and is copolymerizable therewith in aqueous emulsion. topolymerization in aqueous emulsion in the presence of a water soluble salt of a heavy metal occurring in group VIII and the first long period of the periodic table, and an allphatic polycarboxylic acid containing from two to three carboxyl groups and no additional structure other than aliphatic structure in which there is present, in addition to hydrocarbon structure,

no structure other than hydroxy.

' 3. The method which comprises subjecting a monomeric mixture of a conjugated butadiene and another compound which contains a asaaava metal salt and an aliphatic polycarboxylic acid containing from two to three carboxyl groups and being otherwise composed, in addition to the carboxyl groups, exclusively of aliphatic hydrocarbon' structure. 3

4. The method which comprises subjecting a monomeric mixture of butadiene and a compound which contains a group and is copolymerizable therewith in aqueous emulsion, to polymerization in aqueous emulsion in the presence of a water soluble salt of a heavy metal occurring in group VIII and the first long period or the periodic table. and an aliphatic dicarboxylic acid containing less than six carbon atoms and being composed, in addition to its two carboxyl groups, exclusively of aliphatic hydrocarbon structure.

5. The method which comprises polymerizing butadiene in aqueous emulsion in the presence of a heavy metal catalyst obtained by the combination of a water soluble salt of a heavy metal occurring in group VIII and the first long period of the periodic table, and an aliphatic dicarboxylic butadiene in aqueous emulsion in the presence of a heavy metal catalyst obtained by the combination of a water soluble salt of a heavy metal occurring in group VIII and the first long period of the periodic table, and an aliphatic dicarboxylic acid containing less than six carbon atoms and having its two carboxyl groups connected together by an alkyiene radical.

9. The method which comprises polymerizing a mixture of butadiene and acrylonitrile in aqueous emulsion in the presence of a water soluble cobalt salt and an alkali metal salt of iumaric acid.

10. The method which comprises polymerizing a conjugated butadiene in aqueous emulsion in the presence oi? a water soluble complex compound of a heavy metal occurring in the 6th to 12th positions of the first long period of the periodic table and an aliphatic polycarboxylic acid containing from two to three carboxyl groups and being otherwise composed, in addition to the carboxyl groups, exclusively of aliphatic hydrocarbon structure.

ll. The method which comprises polymerizing a conjugated butadiene in aqueous emulsion in the presence of hydrogen peroxide, a fatty acid.

soap and a heavy metal catalyst obtained by the combination of a water soluble salt of a heavy metal occurring in group VIII and the first long period of the periodic table and an aliphatic polycarboxylic acid containing from two to three carboxyl groups and no additional structure other than aliphatic structure in which there is present, in addition to hydrocarbon structure, no structure other than hydroxy.

WILLIAM D. STEWART. 

